When Alexandre gets out of the water to go help Margot in the beginning, his attacker hits him twice with the bat. Towards the end, when they show this same attack from farther away his attacker hits him thrice.
Alex gets an email with the tips user: "concert" + password: "olympia", but he gets no access to the email account. Afterwards, when he hears a U2 song ("With Or Without You") he recalls a past experience with his wife and tries to log in with user: "U2" + password: "1995" which grants him access.
The fact is that U2 only played live three times in 1995, they were no full concerts, and none of them was held at a venue called "Olympia".
Early on in the film at a show jumping scene, the announcer says the video screen shows the rider winning at the European championships, but the video shows the rider jumping over jumps with the Olympic logo on them.
Bruno's black SUV has German license plates. The front plate shows the characters "KLE C 350" ("KLE" stands for the town of Kleve), the rear plate is incorrectly "350 KLE C". German license plates always begin with one to three letters which indicate the county where the car is registered, followed by one or two characters and one to four numbers at the end. German plates never begin with numbers.
At one point in the movie the main character is on Yahoo mail; As he logs in the password he types ("olympia") appears in full letters, while in reality it would be hidden (you would only see "*******").
While technically the Firefox browser does have a plugin that reveals inputs in the password field, one can assume that most people don't use Firefox, much less have the plugin installed.